In the SEM observation of an insulating-substance composed sample by using a charged particle beam, the main object and concern has been placed on elimination or neutralization of the electrification which turns out to become the problem. In order to accomplish this object, the following techniques and units have been disclosed so far, for example: A technique for converting an insulating-substance sample into electrically conductive property by forming an electrically conductive layer on the insulating-substance sample by a method such as evaporation (Patent Document 1), a technique for neutralizing the electrification on the insulating-substance sample by providing an irradiation unit of beams such as an electron beam or positive and negative ion beams independently of a primary charged particle beam which is irradiated onto the sample for forming the image (Patent Documents 2 and 3), a technique for neutralizing the electrification by providing a plasma irradiating unit inside a sample chamber or outside the sample chamber (Patent Document 4), a unit for maintaining the inside of the sample chamber under low vacuum (Patent Documents 5, 6, and 7), a technique for neutralizing the electrification by providing a gas locally-introducing unit (Patent Document 8) to ionize the gaseous molecules by the primary charged particle beam, and further, a technique for converting the insulating-substance sample into the electrically conductive property by irradiating short-wavelength light such as ultraviolet rays onto the electrified area (Patent Documents 9 and 10). Any of the above-cited techniques and units, however, has the following drawbacks: An on-the-spot observation is impossible to make, the throughput is low, the device control is complicated, the resolution is low, the maintenance is difficult and the period is short, a photosensitive material such as resist is unsuitable therefor, and the like.
Meanwhile, as a technique similar to the configuration of the present invention, a defect inspection method for an insulating-film sample in the SEM has been disclosed in Patent Document 11. This defect inspection method is as follows: Namely, an electrode is located in a manner of being directly opposed to the sample, then applying an appropriate electric voltage thereto. This voltage allows low-energy secondary electrons generated from the sample to be fed back to the sample, thereby making it possible to stabilize the electrification at a constant potential. Accordingly, it has been publicly known that the electrification can be relaxed by using the secondary electrons via the operation of the electrode. This technique, however, is an invention belonging to the era where the device size was larger. Moreover, the electron-beam irradiation area in question is also larger than the one in the present invention. Namely, the effect which this technique brings about is, after all, an effect of roughly suppressing an in-elapsed-time increase in positive electrification on the insulating film. This technique is also a one which was used afterwards for the potential contrast control over a circuit inspection device called “EB tester”. After all, this technique differs from the present invention in its objects and effects. In the present invention, controls to be implemented are as follows: A control over local displacement of the electrification charges, a control over the beam drift whose velocity is equal to a few nm/s and which is caused by the potential gradient on the insulating-substance sample, and a dynamic control over the electrode voltage where attention is focused on an intentional control over the potential barrier. These controls and phenomena turn out to become problems when making a high-magnification and high-accuracy length-measurement just like in the present invention.
Also, in Patent Document 12 and Patent Document 13, disclosures have been made concerning observation methods for the insulating-substance sample. The observation methodologies described in the above-described Documents are as follows: Here, in general, the retarding method is a high-resolution implementation methodology for the SEM where a primary electron beam with high energy supplied is caused to pass through within a lens field which functions as a deceleration potential against the primary electron beam. In the device where the retarding method is used for a sample or a sample stage, an electrode is located at a position above the sample or in such a manner as to cover the sample, then applying thereto a voltage which is equal to the retarding voltage. This voltage allows the sample to be positioned within an electric-field-absent environment, thereby controlling the insulating-substance sample surface at an arbitrary potential. Otherwise, in the device which uses the retarding method, an auxiliary electrode is added with an object of improving yield quantity of the secondary electrons. These methodologies, however, differ from the present invention in the following points: Namely, the control over the electrification and a reduction in the beam drift are not regarded as their object, and such an effect itself cannot be expected.
Moreover, in Patent Document 14, a disclosure has been made concerning the following configuration: In the SEM which uses the retarding method, an objective-lens polar segment is located, and also an intermediate electrode is located at a position above the objective-lens polar segment. The intermediate electrode is a technique for neutralizing the electrification of a sample by applying a negative bias to the objective-lens polar segment to cause the secondary electrons generated from the sample to be fed back to the sample. However, the present configuration itself has been disclosed in the above-described Patent Document 13. Also, the principle and the phenomena have been disclosed in the above-described Patent Document 11. Accordingly, since the effect of the sample stage lacks in the conventional techniques, it is impossible to make uniform the potential gradient on the sample surface. Simultaneously, with the contents disclosed as the present configuration, it is difficult to implement the stabilization of the electrification on the insulating-substance sample, and the inspection and length-measurement in the high magnification where the beam drift turns out to become the problem. Consequently, no concrete solving unit or method has been disclosed for these problems.    Patent Document 1: JP-A-8-68772    Patent Document 2: JP-A-8-222176    Patent Document 3: JP-A-10-172493    Patent Document 4: JP-A-2002-131887    Patent Document 5: JP-A-9-304040    Patent Document 6: JP-A-5-174768    Patent Document 7: JP-A-2002-203774    Patent Document 8: U.S. Pat. No. 6,555,815B2    Patent Document 9: JP-A-2000-36273    Patent Document 10: JP-A-10-312765    Patent Document 11: JP Pat. 2130001    Patent Document 12: JP-A-09-171791    Patent Document 13: JP-A-2001-026719    Patent Document 14: JP-A-2002-250707    Non-Patent Document 1: A DATABASE OF ELECTRON-SOLID INTERACTIONS David C Joy, EM Faculty, University of Tennessee, and Oak Ridge National Laboratory